| Natural WPI is a globulin, there are many -OH and -SH conceal in it,and seldom crosslinking between molecules.Simplex Whey Protein form complete film difficultily because of intrinsic structure constraint.After heat treatment,-OH and-SH inside whey protein were emerged by adding plasticizer and reducing agent,which promote forming -S-S- during whey protein solution drying process,and the optimal performances of edible film was obtained.Four typical modified films(A,B,C,D) were choosed to analyze structure and utilize.Through the single factor experiment confirmed optimum concentration of WPI,the best content of glycerin and cysteine.Four factor three horizontal orthogonal experiment was carried base on single factor experiment, the order of factors effect was gotten by weighting scoring method, that was: content of glycerin) concentration of WPI) heating temperature) heating time. Optimum resultants were concentration of WPI 8%,the content of glycerin 4%,the content of cysteine 0.6mmol/L, heating temperature 85℃,heating time 20min.The WPI film scores was 84.5 on optimum condition.The optimum addition of TG,the best pH,the best reacting temperature and the optimum reacting time were gotten from single factor experiment.Four factor three horizontal orthogonal experiment was carried base on the single factor experiment the order of factors effect was gotten by weighting scoring method, that was:concentration of WPI) addition of TG) reacting temperature) pH. Optimum resultants were concentration of WPI 8%, content of glycerin 4%, content of cysteine 0.6mmol/L, heating temperature 85℃, heating time 20min,cool down ordinary temperature,add 40U/g TG,adjust pH7.0,react 60min under 50℃. The WPI film scores was 93.7 on optimum condition.P-Lg and a-La were aggregated to form large oligomer and small amounts of polymer by adding a small quantity of enzyme from SDS-PAGE test.Because of sufficient enzyme adding large P-Lg and a-La were aggregated,the quantity of oligomer changed a little,but a great quantity of polymerwas formed.Film structure wes observed with SEM,from A film to D film,the cross section of was more compact, less vacant space,the minipores in the surface of film were less,there is no minipores in the surface of D film.After adding reducing agent,the cross section of film structure changed from rugosity and rough to uniform porous network structure,the minipores in the surface of film changed from many to small amounts;The cross section of film structure was more compact,but the surface of film was uneven with rare minipores by adding a small quantity of enzyme.Adding sufficient quantum of enzyme, the cross section of film structure was more compact and form threadlike network structure,the surface of film was smooth and glossy without minipore.There were two aspects on applications of WPI films.First, WPI films was used fore refreshing fruit.From A group to D group, weightless rate of saintess fruit less than blank group were 3.24%,4.95%,6.60%,10.46%, which demonstrated the hinder watercraft of films were improved significantly.The other was the performances of WPI films pouch package.The tested heat-sealing strength was enhanced significantly from A film to D film.The water tolerance was tested.A,B,C,D WPI films were insolubilize for 30 minutes in boiling bath,films have very strong water tolerance,this provide theory basis for film application on liquid package.
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